This invention relates to liquid crystal display (LCD), in particular to the method of making an LCD cell.
A liquid crystal display device as shown in FIG. 1 is composed of a pair of glass substrates with electrical conducting patterns enclosing an array of thin film transistor picture elements (TFT pixels) 3. The paired glass substrates 2, each having an orientation film, are arranged opposite to each other at a space defined by spacers and are sealed by an adhesive sealing material 2 to form a cell structure. An organic polymer film 4, such as polyimide film which is most widely used, can be used as an alignment film. In general, polyimide is obtained from heating polyamic acid, which is a precursor of polyimide, at high temperature such as 300.degree. C. to cause imidization. Conventional method of making alignment film is using an Asahi Photosensitive Resin (APR) plate to print polyimide or polyamic acid solution on the surface of the glass substrate at first, and followed by evaporating out excess solvents and curing at high temperature. However, polyimide alignment films obtained from this process have severe shrinkage which results in crowning of plating structure around the film edge. For example, the cured polyimide film with thickness of 600.about.900 A.degree. has about 800.about.1000 .mu.m shrinkage in dimension from its original boundary for a 3"LCD cell, depending on the heating condition and polyimide type. The printing error of an APR plate to the glass substrate is around 100 .mu.m. It is desirable not to have any polyimide films underneath the sealing band area due to poor adhesion between the polyimide and the sealing material. Moreover, polyimide film outside the seal band absorbs environmental moisture and results in poor reliability. Any poor seal in LCD cell can result in poor optical performance, poor reliability, and liquid crystal leakage, In order to increase the sealing reliability of the LCD cell, it is necessary to make the uncontacted area of the sealing material 5 with the polyimide alignment film 4 as large as possible. However, the enlargement of the uncontacted area is restricted due to dimensional limitation in the design of the LCD cell. Hence, for a conventional LCD design, there is a gap 1 (FIG. 1) around 800.about.1000 .mu.m between the LCD seal and the display pixel to assure that there is no polyimide film under the seal band. Recently, there are increasing demands for a greater display panel size and for an improvement in the LCD quality and reliability. From the above mentioned problems, a well controlled dimension for polymer alignment film is very difficult to obtain in conventional manufacturing method but is very important for the LCD quality.